Recent cellular systems provide packet data services, as well as basic voice communication service, through the interoperability with packet-switched data networks. Typically in the wireless communication system such as Wideband Code Division Multiple Access (WCDMA) system supporting data services, the data services are provided through the service provider's network such that the data traffics are concentrated to the service provider's network.
In case of a WCDMA system providing the subscribers with internet access service, the packet data transmitted by a User Equipment are delivered to an IP router through a Node B, a Radio Network Controller (RNC), a Serving GPRS Support Node (SGSN), and a Gateway GPRS Support Node (GGSN). In this case, since the user data are routed through a tunnel established between the RNC to the GGSN using a GPRS Tunneling Protocol (GTP) which operates unlike the typical IP routing protocols, IP routers placed on the link between the RNC and GGSN do not know the content of the data. This means that the packet data transmitted by the user must pass across the GGSN, i.e. the operator s IP router regardless of the location of the Internet server which the user wants to access. However, this IP packet routing method is very inefficient as compared to the normal IP routing method. In such a network structure, the concentration of the traffic load to the network increases significantly as the packet data traffic increases.
A home networking service can be another example as a packet data service provided through a cellular network. In Long Term Evolution (LTE) as an evolved 3GPP mobile communication technology, a Home evolved Node B (HeNB) is defined as a femto cell to support LTE air interface, and researches are being conducted to control electric appliances and play audio and video data remotely using a User Equipment (UE) connected to the HeNB. Here, the HeNB can be defined as a femto base station similar to a DSL router and a cable modem to provide cellular coverage in a subscriber's home or small business and provides cellular coverage very small as compared to a macro Node B (macro NB). In the current LTE network architecture, however, the data transmitted to the HeNB must be delivered across the operator's network such that even the local traffic leaves the current region and then back into the home network unreasonably.
As aforementioned, the conventional mobile communication systems supporting IP-based data services deliver even the local traffic through the operator's network, and thus the local traffic delivered through inefficient routing paths increases traffic load unnecessarily from the viewpoint of the operator's network and causes transmission latency from the viewpoint of the home networking service.
Recently, the use of the packet data services of the mobile communication system tends to increase rapidly in various fields, whereby an efficient local traffic handling mechanism is becoming one of the significant issues to be addressed in the cellular communication supporting packet data service.
FIG. 1 is a diagram illustrating an Evolved Packet System (EPS) architecture for 3GPP access. EPS is a packet-optimized system evolved from the Universal Mobile Terrestrial System (UMTS). The EPS is also termed System Architecture Evolutions and the terms are interchangeable used. The SAE system includes an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) 103, a Mobility Management Entity (MME) 113, a Serving Gateway (S-GW) 105, a Policy Control and Charging Rules function (PCRF), and a Packet or Public Data Network (PDN) Gateway (PGW) 107.
The E-UTRAN 103 is an evolved access network and includes an evolved Node B (eNB). The MME 113 is responsible for terminating Non Access Stratum (NAS) signaling, NAS signaling security, UE mobility management, idle mode UE management, roaming, authentication, and bearer management. The SGW 105 is responsible for local mobility anchor function for inter-eNB handover, inter-Radio Access Technology (RAT) anchor function, idle mode downlink packet buffering function, and lawful interception (LI). Here, the LI means eavesdropping of IP with lawful authorization. The PGW 107 is responsible for policy enforcement, per-user based packet filtering, charging support, LI, UE IP address allocation, and packet screening function.
The PCRF 111 is responsible for management of service-specific policy control and Quality of Service (QoS). The SGSN 115 is an entity of the legacy packet network and responsible for controlling services related to the UEs. For instance, the SGSN 115 is responsible for manages the billing data per UE and provides the UE with the service-specific data. The HSS 117 is responsible for managing the subscriber information and location information.
The above-described network entities can support additional functions depending on the supportable services.
Assuming that the server within an IP network which the UE wants to access is located near the current location of the UE, e.g. the server is placed in the network where the eNB is, the data packet generated by the UE is transmitted to the PGW outside the network and then delivered to the server within the network of the eNB according to the normal IP routing method.
FIG. 2 is a sequence diagram illustrating operations of entities when a UE requests the network for an additional IP address in the conventional wireless communication system.
Referring to FIG. 2, first the UE 101 sends the MME 113 a PDN Connectivity Request message including an Access Point Name (APN) designated for the network to access (201). Upon receipt of the PDN Connectivity Request message, the MME 113 verifies the APN with the subscription information and selects, if the APN is verified, a PGW 107 indicated by the APN for providing PDN service. Once the PGW 107 is selected, the MME 113 sends a Create Default Bearer Request message including the address of the PGW 107 to the SGW 105 (203). The SGW 105 forwards the Create Default Bearer Request message to the PGW 107 (205). If the Create Default Bearer Request message is received, the PGW 107 performs a PCRF interaction with the PCRF 111 for acquiring the policy and charging control (PCC) rule for the UE 101 (206).
After the completion of the PCRF interaction, the PGW 107 assigns an IP address to the UE 101 and sends a Create Default Bearer Response message including the UE IP address to the SGW 105 (207). The SGW 105 forwards the Create Default Bearer Response message to the MME 113 (209). The SGW related information includes the IP address of the SGW 105 and Tunnel Endpoint Identifiers (TEIDs) of the control and user planes. Upon receipt of the Create Default Bearer Response message, the MME 113 sends a PDN Connectivity Accept message including the IP address assigned by the PGW 107 to the UE 101 in response to the PDN Connectivity Request message transmitted by the UE 101 at step 201. In more detail, the MME 113 sends a Bearer Setup Request message including the PDN Connectivity Accept message to the eNB 102 (211), and the eNB 102 sends a Radio Resource Control (RRC) Connection Reconfiguration message including the PDN Connectivity Accept message to the UE 101 (213).
Upon receipt of the RRC Connection Reconfiguration message, i.e. the PDN Connectivity Accept message, the UE 101 sends an RRC Connection Reconfiguration Complete message to the eNB 102 (215). The eNB 102 received the RRC Reconfiguration Complete message sends a Bearer Setup Response message to the MME 113 (217). The MME received the RRC Reconfiguration Complete message sends an Update Bearer Request message including the IP address of the eNB 102 and the user plane TEID to the SGW 105 (219), and the SGW 105 sends an Update Bearer Response message to the MME 113. As a consequence a GTP tunnel is established between the eNB 102 and the SGW 105 for tunneling the data packets.
According to the procedure described with reference to FIG. 2, the GTP tunnel is established between the eNB 102 and the PGW 107 such that the data transmitted by the UE delivered to the IP network through the eNB 102, SGW 105, and the PGW 107 and the data received from the IP network is delivered to the UE 101 in reverse order.
In the cellular system using this conventional packet transmission method, however, all the packet data transmitted by the UE are delivered to the server via the PGW 107 regardless of the location of the server, whereby the local data packets destined to the server locates near the eNB experience unnecessary propagation delay.